Convert APK to ASEC

The only way how it might be perhaps possible to create encrypted Android packages (.asec) out of ordinary Android packages (.apk) is to install Android SDK tools and use these to encrypt the packages. On some phones it is also possible to simply download the APK package on your smartphone to the SD card, which should also change the format from APK to ASEC, but dedicated apk to asec converter most likely does not exist.